Actuators to open and close gate valves for high pressure uses may include manual operators, diaphragm-type operators, hydraulic operators or pneumatic operators. Typically, such actuators include a bonnet assembly which connects a gate valve body, a valve gate and a bonnet stem to the actuator body. Still further an operator is connected to the gate and associates with the actuator to open or close the gate valve. The operator typically has a maximum force capability for applying to the bonnet stem. It is sometimes desirable to change the opening/closing power of an actuator for different gate valve operations involving different fluids at different pressures without having to remove the actuator itself.
Regarding gate valves, these valves are generally comprised of a valve body having a central axis aligned with inlet and outlet passages, and a space between the inlet and outlet passages in which a slide, or gate, may be moved perpendicular to the central axis to open and close the valve. In the closed position, the gate surfaces typically seal against sealing rings which surround the fluid passage through the valve body. Gate valves have been used for centuries to control the flow of a great variety of fluids. Often the fluid to be controlled by the gate valve is under pressure. In the petroleum industry, gate valves are used along piping at various locations, and in particular are used in piping referred to in the petroleum industry as a Christmas tree, which is used as part of a drilling operation.
Hydraulic actuators typically incorporate a single piston and cylinder to produce a force in pounds per foot or kilograms per meter to open or close a gate valve. Typically the media used in hydraulic actuators is a standard hydraulic fluid, although other fluids may be used in particular applications. Many hydraulic actuator producers will designate optimum parameters for piston applications to cover the complete size range of gate valves. However, certain markets require specific pressures and volumes to be utilized. By adding or subtracting the diametrical size of the piston, the volumes and pressure can be increased or decreased.
Given the range of pressures and volumes that are required for different valve actuation using a hydraulic piston actuator, it would be advantageous to develop an actuator capable of switching piston diameters without swapping out hydraulic actuators on a given gate valve. Additionally, by switching out pistons on a hydraulic actuator companies could save money and resources by creating a single hydraulic actuator with interchangeable parts.